One of the main causes of tire noise is cavity resonance created in the cavity of a pneumatic tire that is airtightly formed between the rim of a wheel and the tire mounted on the rim. The cavity resonance participates in, for example, noise we constantly hear near 250 Hz during running, and impact sounds produced in passing the joints of a road or the like.
As an approach for reducing noise created by such cavity resonance, it has been proposed to place a sound absorbing member in the cavity of a tire to absorb the resonance noise, or to provide shielding plates on a rim so as to section the cavity of a tire. However, since the sound absorbing member is not one that fundamentally restricts the occurrence of the cavity resonance, noise can not be effectively reduced with a sound absorbing member that can actually be mounted on the inside of a tire. In the case where the shielding plates are mounted on a rim, performance of assembling a tire on the rim is deteriorated.
Recently, there has been proposed a tire cavity resonance restricting device that can effectively reduce the cavity resonance noise by constantly varying the frequency of the resonance with the rotation of the wheel by changing the cross-sectional shape of the tire cavity in the tire circumferential direction (see Patent Documents 1 and 2). However, a tire having the tire cavity resonance restricting device has uneven mass distribution around the circumference, which produces a problem of assisting tire vibration during running of a vehicle.
Patent Document 1: Japanese Patent Application Kokai Publication No. 2000-113902
Patent Document 2: Japanese Patent Application Kokai Publication No. 2003-226104